Thermal responsive switch



March 18 ,1924.

l. HALL THERMAL RESPONS I VB SWITCH Filed May 2, 1921 um m m w e o Q m hA C s .H w

Patented Mar. 18, 1924.

1,4 1,515 PATENT orncs.

CHESTER I. HALL, OF FORT WAYNE, INDIANA, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

THERMAL RESPONSIVE SWITCH.

Application filed May 2,

To all whom it may concern:

Be it known, that I, CHESTER I. HALL, a citizen of the United States,residing at Fort Wayne, in the county of Allen, State of Indiana, haveinvented certain new and useful Improvements in Thermal ResponsiveSwitches, of which the following is a specification.

Myinvention relates to improvements in" thermal responsive switches andin particular to improvements in thermal responsive time switches.

One of the objects of the invention is the provision of a switchwhichwill operate in a definite and predetermined time due to a flow ofcurrent of a definite value.

Another object of the invention is the provision of a switch of thecharacter indicated which will operate quickly by a snap action.

Another object is the provision of a switch of the character indicatedwhich will be operated substantially independently of variations ofambient or room tempera ture.

The invention has a particular utility in the control of the timing ofX-ray exposures with relation to either the current taken by the tube orthe applied potential. However, the invention is by no means limited toits use in the control of X-ray exposures, but is applicable generallyto give a thermal time element control of an electric circuit.

In carrying the invention into effect in one form, a thermostatic latchis provided which is flexed responsively to the heating effect of apredetermined value of current to release a switch member to quicklyreturn to its normal position after an interval of time. The timeinterval may be very nicely varied by varying the relative positions ofthe switch member and the thermostatic latch. A heating elementpreferably either a coil mounted on the thermostatic latch or in closeproximity thereto, is provided for heating the latch in accordance withthe current through the switch. A thermal responsive member is connectedto the latch for the purpose of compensating for changes ofambient-temperature and a cam cooperates with the member for varying thetime taken to open the switch. The switch parts are enclosed in a.casing which provides a thermal storage volume so that the same lengthof time will always be required for 1921. Serial No. 486,335.

'and arrangement; Fig. 2 is a side view'of the same with the cover ofthe case in section; and Fig. 3 is a very simplified diagram of acontrol arrangement for an X-ra tube with my improved thermal time switcshownin simplified diagram controlling the time of the X-ray exposurefor value of current.

Referring to the figures, the switch member is pivoted at 11 and hasconnected therewith a resiliently mounted switch contact 12 which isadapted to make engagement with the stationary contact 13 to complete anelectric circuit through the switch. The switch member 10 and theresiliently mounted contact 12 are biased to the open position by meansof the spring 1& and are held in the closed position against the bias ofthe spring 14 by means of the thermostatic latch 15. This thermostaticlatch is adapted to be heated in accordance with the current through theswitch contacts 12 and 13 by means of a heating coil 16 insulated in anysuitable manner from the thermostatic latch and connected at one end 17to the latch. This thermostatic latch is supported in an insulatingblock 18 which is pivotally mounted on the pin 19, and a thermalresponsive member 20 is connected to the latch so as to compensate forchanges of ambient temperature. The free end of the thermostatic latchis adapted to make an abutting engagement with the switch member 10 sothat this free end may slide freely with respect to the switch member.

A rotatable cam 21 cooperates with the thermal responsive member so asto vary the relative positions of the member 20'and the latch 15 withrespect to the switch member 10 so as to adjust the point of abutment ofthe free end of the latch and predetermine the length of time taken'bythe latch in bending or flexing so as to slide out of a given engagementwith the switch member 10 and thereby release this switch member to openthe switch contacts 12 and 13. The cam 21 is mounted on a shaft- 22which extends through the cover of the casing 23, and a knob 2% isprovided on the end of the shaft 22 for turning the cam 21 from theoutside of the casing. 1 pointer 25 is also mounted on the shaft 22 andcooperates with the scale on the cover of the casing to indicate thetime taken by the switch in opening for a given value of current. Aspring 27 is proi'ided for biasing the thermal responsive member 20 intoengagement with the cam 21. A button 28 of insulating material extendsthrough the casing and is adapted to engage the extension 29 on the endof the switch member 10 so as to return the switch member to the closedposition after it. has been opened in response to the bend ing orflexing of the thermostatic latch 15. This button is biased out ofengagement with the casing of the switch by means of the spring 30. Theswitch parts are suitably mounted on the base 23' of insulatingmaterial. By reason of the factv that the switch parts are enclosedwithin the casing 23. a thermal storage volume is provided, so thatsubstantially the same length of time will always be required for thesame deflection of the thermostatic latch. The thermal responsive member20 will compensate for changes of ambient temperature by reason of thefact that this member and the thermostatic latch will always bend orflex in the same direction due to a change of ambient temperature, andthe flexing of the member 20 will thus counteract the flexing of thelatch.

Referring to Fig. 3, the thermal responsive switch previously describedis adapted to control the primary 31 of a transformer, the secondary 32of which is connected to the terminals of the X-ray tube 33. The righthand terminal of the secondary 32 is connected to an anode or target 34of the X- ray tube, and the hot cathode 35 of the tube is connectedacross a portion 32' of the secondary of the transformed. An adjustableresistor 36 is provided for varying the potential applied to the hotcathodes 35. The ammeter 37 is connected in the circuit of the secondarof the transformer for indicating the current in the secondary circuit.

The operation of my invention as thus constructed and arranged is asfollows:- Assume that the switch is in the closed position as indicatedin the figures and thatthe pointer 25 has been turned to the properposition to indicate the time of X-ray exposure desired. The heatingcoil 16 will heat the thermostatic latch 15 substantially in accordancewith the current through the switch contacts 12 and 13, and this latchwill flex or bend so that finally the free end of the latch will bemoved out of enga ement with the switch member 10. T is switch member 10has a channel section so that the abutting free end of the therinostaticlatch 15 will slide along the switch member 10 and finally leave theright hand end of the switch member. The switch member is then permittedto return to the open position by reason of the bias of the spring 1eand carry the resiliently mounted contact- 12 quickly out of engagementwith the stationary contact 13 by a snap action. The time interval takenby the switch in opening will be substantially identical with the timeas indicated on the scale 26 for a given value of current, by reason ofthe fact that the various parts of the switch are enclosed within thecasing 23, and also by reason of the fact that variations of ambient temperature are compensated for by the cooperation of the thermalresponsive member 20 with the thermostatic latch 15. When the switchopens, the X-ray bulb 33 is'simultaneously deenergized and the exposureof the X-rays ceases.

In order to reset or close the switch, the button 28 will be pressed soas to return the switch member 10 and the resiliently mounted contact 12to the closed position, thereby permitting the thermostatic latch 15 toslip past the end of the switch member and return to its originalposition. It will be understood that the thermostatic latch will resumeits initial shape shortly after the heating coil 16 is deenergized bythe opening of the switch contacts.

In order to obtain a greater or less time interval for agiven value ofcurrent, the knob 24 will be turned to the desired time interval asindicated on the scale 26, thereby moving the cam 21, the thermalresponsive member 20 and the thermostatic latch 15 so that they aremoved to different relative positions with respect to the switch member10 and the point of abutment of the free end of the latch is varied. Theshape of the cam 21 is such that a substantially uniform scale 26 may beprovided. Obviously. if the value of the current is varied, the timelimit for a given setting will be correspondingly varied, so that theswitch may be used to protect a translation device from overheating.

It is to be understood that while I have indicated a use for myinvention in the control of the time for X-ray exposure, my invention isnot necessarily limited thereto, but is applicable generally to give a.thermal time element control of any electric circuit.

In accordance with the provisions of the patent statutes I havedescribed the principle of operation of my invention, together with theapparatus which I now consider to represent the best embodiment therof,but I desire to have it understood that the apparatus shown is onlyillustrative and that the invention can be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is 1. The combinationin an electric switch of a switch memberbiased to a normal position. a pivo-tally supported flexiblethermostatic latch adapted to engage the switch member for holding theswitch member in another position, the said latch adapted to be flexedrcsponsively to the heating effect of a predetermined value of currentto thereby disengage the switch member and release the same to return tothe normal position after an interval of time, and means for adjustingthe position of the latch about its pivotal support for varying the saidtime interval.

2. The combination inan electric switch of a switch member biased to theopen position, a. pivotally supported flexible thermostatic latch havinga free end adapted to.

abut against the switch member for holding the same in the closedposition, a heating coil disposed on the latch for heating the latch inaccordance with the current through the switch to thereby flex the latchand cause the free end thereof to slide out of abutting engagement withthe switch member and release the switch member after an interval oftime, and means for adjusting the position of the said} latch about itspivotal support for Varying the said time interval.

3. The combination in an electric switch of a movable switch memberbiased to the open position, a resiliently mounted switch contactcarried thereby, a flexible thermostatic latch adapted to engage theswitch member for holding the switchmember and contact in the closedposition, an electric heating element for the said thermostatic latch,the said latch adapted to be flexed responsively to the heating effectof the said heating element to disengage the switch member and releasethe same to return to the open position, and means for imparting a.relative movement to the said latch and the said switch member foradjusting the time mounted switch contact carried thereby, a

flexible thermostatic latch one end of which is supported and the freeend of which is adapted to abut against the switch member for holdingthe switch member and the said contact in the closed position, an.electric heating element for the said thermostatic latch, the said latchadapted to be flexed responsively to the heating effect of the saidheating element to cause the free end of the latch to slide out ofabutting engagement with the said switch member and release theswitclrmember to return to the open PO itime taken by the latch torelease the switch.

member for a given value of current in the heating element.

5. The combination in an electric switch of a switch member biased to anormal position, a flexible thermostatic latch for holding the switch.member in another position and arranged to flex responsively to theheating effect of a predetermined value of current to release the.switch member after an interval of time, and a thermoresponsive memberconnected to the latch for compensating for changes of ambienttemperature.

6. The combination in an electric switch of a switch member biased to anormal position, aflexible thermostatic latch for-holding the switchmember in another position and arranged to flex rcsponsively to theheating effect of a predetermined value of current to release the switchmember after an interval of time, a thermoresponsive member connected tothe latch for compensating for changes of ambient temperature, and meansfor varying the relative positions of the latch and the thermoresponsivemember with respect to the switch member for varying the time taken bythe latch to release the switch member for a given value of current.

7. The combination in an electric switch of a switch member biased tothe open position, a flexible thermostatic latch one end of which isadapted to engage the switch to hold the same in the closed position, athermostatic strip having one end connected to the other end of thelatch and adapted to be held in position for compensating for changes ofambient temperature, and a pivotal support for the connected ends of thestrip and latch.

8. The combination in an electric switch of a switch member biased tothe open position, a flexible thermostatic latch one end of which isadapted to engage the switch member to hold the same in the closedposition, a thermostatic strip having one end connected to the other endof the latch, and means for rotating the latch and strip about theirconnected ends as a pivot for varying the time taken by the latch torelease the switch member for a given value of current.

9. The combination in an electric switch of a switch member biased tothe open posi- III 311M) combmatwn in an lectl'ic- 7 herem a w switchcon tact connectei 131: 11 1s adapted to engage th

